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Comets

Not long ago, many people thought that comets were a sign that
something bad was about to happen to them. People didn't
understand how objects in the sky moved, so the sight of a comet must have been very disturbing. There are
many historical records and works of art which record the appearance of
comets and link them with terrible events such as wars or plagues.

Now we know that comets are lumps of ice and dust that periodically
come into the center of the solar system from somewhere in its outer
reaches, and that some comets make repeated trips. When comets get close enough to the Sun, heat makes them start
to evaporate. Jets of gas and dust form long tails that we can see from Earth.
These tails can sometimes be millions of miles long.

In 1985-1986, a spacecraft called Giotto visited the most famous comet,
Halley, on Halley's most recent visit to the inner solar system. In 1994, comet Shoemaker-Levy became trapped by the gravity of Jupiter and plunged into Jupiter's atmosphere!

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When comets are kicked out of the Oort Cloud, they begin a passage into the solar system, spinning and tumbling as they come. The trajectory which they acquire can be hyperbolic, parabolic, or elliptic...more

Hale-Bopp continues to offer new surprises as two astronomers report of their study of the comet. Using the Hubble Space Telescope and the International Ultraviolet Explorer, the astronomers did a year-long...more

Stardust is the name of a space mission that studied a comet. NASA's Stardust spacecraft flew past a comet named Wild 2 in January 2004. During its flyby Stardust collected some dust particles from the...more

Comet Wild 2 is named after the scientist who discovered it. Paul Wild is an astronomer from Switzerland who discovered the comet in January 1978. Wild 2 is pronounced "Vilt 2". The comet orbits the Sun...more

Comet 67P/Churyumov-Gerasimenko was discovered in 1969 by Klim Churyumov and Svetlana Gerasimenko. The comet orbits the Sun once every 6.57 years. Its orbit brings it closer to the Sun than Mars at the...more

Anthony Wesley is an amateur astronomer in Australia. On the night of July 19, 2009, Wesley noticed a dark spot on Jupiter that hadn't been there before. He had discovered the remains of a huge impact...more

The picture on this page shows the best views ever of the nucleus of a comet. It shows two pictures of the comet's nucleus that were taken at slightly different times. The pictures were taken by a spacecraft...more